It is well known that phyilosilicates, such as smectite clays, e.g., sodium montmorillonite and calcium montmorillonite, can be treated with organic molecules, such as organic ammonium ions, phosphonium ions, or sulfonium ions (onium ions), to intercalate the organic molecules between adjacent, planar silicate layers, for ion-exchange of the organic onium ion molecules with the interlayer exchangeable cations to space the adjacent layers or platelets of the layered silicate material (interlaminar spacing) sufficiently for intercalation of a polymer between the spaced layers, see, for example, U.S. Pat. Nos. 4,739,007; 4,810,734 and 5,164,460. The thus-treated, intercalated phyllosilicates, having interlayer spacings increased by at least 3 .ANG., preferably at least 5 .ANG., to an interlayer (interlaminer) spacing of at least about 10-25 Angstroms (.ANG.) and up to about 100 .ANG. then can be exfoliated, e.g., the silicate layers are separated, e.g., mechanically, by high shear mixing. The individual silicate layers, when admixed with a matrix polymer, before, after or during the polymerization of the matrix polymer, e.g., a polyamide--see 4,739,007; 4,810,734; 5,102,948; and 5,385,776 --have been found to substantially improve one or more properties of the matrix polymer, such as mechanical strength, oxygen impermeability, and/or high temperature characteristics.
Exemplary prior art composites, also called "nanocomposites", are disclosed in a published PCT application of Allied Signal, Inc. WO 93/04118 and U.S. Pat. No. 5,385,776, disclosing the admixture of individual platelet particles derived from intercalated layered silicate materials, with a matrix polymer to form a nanocomposite having one or more properties of the matrix polymer improved by the addition of the at least partially exfoliated intercalate. As disclosed in WO 93/04118 and U.S. Pat. No. 5,554,670, the intercalate is formed (the interlayer spacing between adjacent silicate platelets is increased) by adsorption of a silane coupling agent or an onium cation, such as a quaternary ammonium compound, having a reactive group which is compatible with the matrix polymer. Such quaternary ammonium cations are well known to convert a highly hydrophilic clay, such as sodium or calcium montmorillonite, into an organophilic clay capable of sorbing organic molecules.
In accordance with a preferred embodiment of the present invention, intercalates are prepared by contacting a layered silicate material, such as a phyllosilicate, with a multi-charged onium ion spacing/coupling agent, such as a di-onium ion spacing/coupling agent compound, and having at least 2 carbon atoms, up to about 24 carbon atoms separating the two onium cations. Exemplary of such suitable multi-charged spacing/coupling agent molecules include quaternary diammonium ions, disulfonium ions, diphosphonium ions, dioxonium ions, or any multi-charged onium ion compound of an element in Groups V or VI of the periodic table of elements.
The multi-charged onium ion spacing/coupling agents useful in accordance with the present invention may be multi-charged upon dissociation of anions from the molecule when dissolved in water and/or an organic solvent, or the molecule may be neutral and subsequently protonated to provide onium ion molecules having multiple positively charged atoms, in solution.
Depending upon the cation exchange capacity of the layered silicate material, e.g., a smectite clay, the interior platelet surfaces of the silicate platelets include negative charge centers that have spacings that vary between about 4 .ANG. and about 20 .ANG. (equal to the spacing, or distance, between adjacent exchangeable cations in the interlaminar space).
In accordance with the principles of the present invention, it has been found that multi-charged onium ion spacing/coupling agents can be intercalated between adjacent platelets to ion-exchange with interlayer cations, e.g., Na.sup.+ ions, to balance the negative charge centers within the same silicate platelet surface, at each properly spaced charged onium ion atom, to space adjacent platelets sufficiently, using less spacing/coupling agent. In the preferred embodiment, at least two of the charged atoms of the multi-charged onium ion spacing/coupling agent are spaced with intermediate organic molecules, e.g., --CH.sub.2 --CH.sub.2 --; --CH.sub.2 --CH.sub.2 --CH.sub.2 ; and the like, to space the charged onium ion atoms (e.g., N.sup..+-. space --N.sup.+) a distance of about 5 .ANG. (for high charge density layered materials) to about 24 .ANG. (for low charge density layered materials). With such preferred spacing between charged onium ion atoms, ion-exchange with interlayer cations occurs at both charged onium ion atoms, thereby necessitating less onium ion intercalation to achieve complete ion-exchange, while achieving sufficient silicate platelet spacing for oligomer or polymer co-intercalation, and permitting co-intercalation of higher quantities of co-intercalant oligomer or polymer.
As shown in FIGS. 1A and 1B, a layered material having a high charge density, having a spacing between adjacent interlayer platelet surface negative charge centers in the range of about 6 .ANG. to about 12 .ANG. can be ion-exchanged at both adjacent charged atoms of a dual-charged onium ion spacing/coupling agent that has the charged atoms spaced a distance of about 4 .ANG. to about 14 .ANG. or 16 .ANG.. The spacing between the closest two charged atoms of the multi-charged onium ion spacing/coupling agent need not be exactly the same as the spacing between adjacent exchangeable cations on the platelet surface of the layered material since each negative charge within and extending above the platelet surface (corresponding to the location of the exchangeable cations) diffuses radially outwardly, from the negative charge center, a distance of about 5 .ANG.. The dashed line circles surrounding the adjacent negative charge centers, as shown in FIGS. 1A and 1B, represent diffusing negative charges that are weaker farther away from the negative charge center, and are located directly above the exchangeable cations, e.g., Na.sup.+, as shown in FIGS. 1A and 1B. Preferred spacing between closest charged atoms of the spacing/coupling agent for high to medium charge density (150 milliequivelents per 100 grams C.E.C.* to 70 milliequivelents per 100 grams C.E.C.*) layered materials is about 6 .ANG. to about 20 .ANG., corresponding to a C.sub.3 to C.sub.10 molecule backbone in the organic spacing molecule between charged onium ion atoms. Preferred spacing between onium ion spacing/coupling agent charged atoms for medium to low charge density (70 milliequivelents per 100 grams C.E.C.* to 30 milliequivelents per 100 grams C.E.C.*) layered materials is about 12 A to about 24 .ANG., corresponding to a C6 to C.sub.12 molecule backbone in the organic spacing molecule covalently bonded to both charged onium ion atoms.
 FNT *Cation exchange capacity.
In accordance with an important feature of the present invention, best results are achieved by mixing the layered material with the (multi-charged spacing/coupling agent, in a concentration of at least about 0.25 moles of onium ion multi-positively charged, cation portion of the onium ion compound) per mole of interlayer exchangeable cations, preferably at least a 0.5:1 molar ratio, more preferably at least 1:1 molar ratio of multi-charged onium ion cation:exchangeable interlayer cations. When less than all of the interlayer cations are ion-exchanged with multi-charged onium ions, the remainder of the interlayer cations can remain in place, or at least a portion of the remaining interlayer cations may be exchanged with single-charged onium ions. For most layered materials, such as sodium montmorillonite clays, the above molar ratios are achieved by intercalating at least about 2% by weight, preferably at least about 5% by weight multi-charged spacing/coupling agent compound, more preferably at least about 10% by weight, and most preferably about 30% to about 200% by weight multi-charged spacing/coupling agent cation, based on the dry weight of the layered material in the intercalating composition. Regardless of the concentration of multi-charged spacing/coupling agent compound in the intercalating composition, the weight ratio of multi-charged spacing/coupling agent intercalant: layered material should be at least 1:20, preferably at least 1:10, more preferably at least 1:5, and most preferably at least about 1:4 to achieve sufficient intercalation of one or more co-intercalants such as oligomer or polymer (or its monomeric reactants) between adjacent inner surfaces of adjacent platelets of the layered material. The multi-charged spacing/coupling agent compound sorbed between and ion-exchanged with the silicate platelets, via ion-exchange at multiple charged atoms, causes surprisingly easy intercalation of a co-intercalant oligomer or polymer, in greater amounts than heretofore possible, or intercalation of increased amounts of monomeric reactants for polymerization in-situ.
In accordance with an important feature of the present invention, it has been found that a multi-charged spacing/coupling agent-intercalated phyllosilicate, such as a smectite clay, can be co-intercalated easily with a co-intercalant polymer to form an intercalate that has unexpectedly superior intercalate dispersibility in a matrix polymer, and unexpectedly can be co-intercalated with higher amounts of co-intercalate polymer molecules. The intercalate also can be added to any other matrix polymer to enhance a number of properties of the matrix polymer, including tensile strength, heat distortion temperature, glass transition temperature, gas-impermeability, elongation, and the like.
The multi-charged spacing/coupling agent-intercalated layered material, that is co-intercalated with a polymer co-intercalant, and/or exfoliates thereof, can be admixed with a matrix polymer or other organic monomer compound(s) or composition to increase the viscosity of the organic compound or provide a matrix polymer/intercalate and/or matrix polymer/exfoliate composition to enhance one or more of the above-mentioned properties of the matrix polymer.
The multi-charged spacing/coupling agent-intercalated layered material and intercalating process of the present invention provide a unique organoclay useful for all known purposes of organoclays, that includes more interlayer space for sorption of organic liquids and gases. Also, in accordance with a preferred embodiment of the present invention, the intercalate can be added, particularly by direct compounding (mixing the intercalate directly into a matrix polymer melt) of the intercalate with any matrix polymer, thermoplastic or thermosetting. Examples of market-available resin systems for use as the co-intercalant polymer and/or the matrix polymer of the nanocomposites include epoxy resins such as: Bisphenol A-derived resins, Epoxy cresol Novolac resins, Epoxy phenol Novolac resins, Bisphenol F resins, polynuclear phenol-glycidyl ether-derived resins, cycloaliphatic epoxy resins, aromatic and heterocyclic glycidyl amine resins, tetraglycidylmethylenedianiline-derived resins, nylons, such as nylon-6 and nylon 66, and particularly MXD6 nylon (meta-xylylene diamine and adipic acid polymerized polyamides).